The turnover rate of acetylcholine was studied in animals exposed to different environmental conditions for different periods of time. Exposure to cold for 1 hour selectively decreased the turnover rate of acetylcholine in the hypothalamus and frontal cortex. A long period of immobilization failed to change the indices of cholinergic activity. Rats were given diets with different choline contents, the turnover rates of acetylcholine brain areas of rats fed with a choline free diet were unaffected whereas the levels of choline were slightly decreased. In rats maintained on a choline rich diet we found a 40 percent decrease in the turnover rate of hippocampal acetylcholine.